Electrolytes for lithium batteries and fuel cells http://www.pa.msu.edu/~duxbury/CND/CND.html January 24th : Jim McCusker (Chemistry - MSU), "Photochemical control of charge transfer complexes for improved solar cells" January 31st : Keith Promislow (Mathematics - MSU), "The role of nanomorphology in proton conduction through polymer electrolytes" February 7th : Greg Baker (Chemistry - MSU), "Materials for Fuel Cells" February 14th : Don Morelli (Materials Science - MSU), "Introduction to high ZT thermoelectric materials and their applications" February 21st : Special Energy Seminar : Wolfgang Bauer (Physics, MSU) Is bio-gas generation a cost-effective option for the Michigan energy economy? February 28th : Phillip Duxbury (Physics - MSU) "Theoretical and practical limits on solar conversion efficiency : Why use nanostructured materials?" Center for Nanomaterials Design and Assembly
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Electrolytes for lithium batteries and fuel cells
http://www.pa.msu.edu/~duxbury/CND/CND.html
January 24th : Jim McCusker (Chemistry - MSU), "Photochemical control of charge transfer complexes for improved solar cells"
January 31st : Keith Promislow (Mathematics - MSU), "The role of nanomorphology in proton conduction through polymer electrolytes"
February 7th : Greg Baker (Chemistry - MSU), "Materials for Fuel Cells"
February 14th : Don Morelli (Materials Science - MSU), "Introduction to high ZT thermoelectric materials and their applications"
February 21st : Special Energy Seminar : Wolfgang Bauer (Physics, MSU) Is bio-gas generation a cost-effective option for the Michigan energy economy?
February 28th : Phillip Duxbury (Physics - MSU) "Theoretical and practical limits on solar conversion efficiency : Why use nanostructured materials?"
Center for Nanomaterials Design and Assembly
Organic (ion-conducting) membranes in energy applications
Li ion batteriessolar cells
supercapacitors
CO2 sequestration
CO2CH4
Fuel cells
Rechargeable Batteries
High reactivity with solvents used for electrolytes -only polyethersare compatible with Li metal
Tarascon, J. M.; Armand, M., 2001, 414, (6861), 359-367
"Rocking Chair" batteries (Lithium Ion Cells)
applications: laptops, cell phones, power tools,
Tarascon, J. M.; Armand, M., 2001, 414, (6861), 359-367
Making batteries is as simple as baking ...
Tarascon, J. M.; Armand, M., 2001, 414, (6861), 359-367
Properties of real lithium batteries
DOE Workshop on Basic Research Needs For Electrical Energy Storage, 2007, http://www.sc.doe.gov/bes/reports/abstracts.html
Advanced batteries
A prototype Lithium-Ion Polymer Battery at NASA Glenn Research Center.
LiCoO2 (Sony)
C-Li(x)
Anode Cathode
Li+
Li+
LiMn2O4 (Bellcore/Telcordia)
Current technology:•liquid electrolyte or gel electrolyte (liquid dispersed in a PVDF gel, allows flat packaging, rather than metal cans).•Li+PF6 or similar salt•mixtures (usually) of ethylene carbonate, dimethylcarbonate, diethyl carbonate
O O
O
H3CO OCH3
O
OO
O
ethylene carbonate
diethyl carbonate
dimethyl carbonate
LiFePO4 (A123 systems)
Flambeau de laptop ...
X-W Zhang, Y. Li, S. A. Khan, P. S. Fedkiw, J. Electrochem. Soc., 2004, 151, A1257-A1263.
Lithium dendrites
Li(1-x)CoO2C-Li(x)
Anode Cathode
LiMn2O4
liquid or polymer electrolyte(flammable! organic )
"....... the theoretical specific energy of a lithium thionyl chloride battery is on the order of 1420 Wh/L, which is comparable to the theoretical specific energy of TNT at 1922 Wh/L."
The moral of the story ....
"....... the theoretical specific energy of a lithium thionyl chloride battery is on the order of 1420 Wh/L, which is comparable to the theoretical specific energy of TNT at 1922 Wh/L."
most organic solvents are inherently unstable to high oxidation and reduction potentials at cathode and anode, small molecule easily transported to electrodes
BASIC RESEARCH NEEDS FOR ELECTRICAL ENERGY STORAGE(DOE Workshop, 2007, http://www.sc.doe.gov/bes/reports/abstracts.html)
suggests polymer-based, ionic liquid, or other solutions
BASIC RESEARCH NEEDS FOR ELECTRICAL ENERGY STORAGE(DOE Workshop, 2007, http://www.sc.doe.gov/bes/reports/abstracts.html)
suggests polymer-based, ionic liquid, or other solutions
a partial wish list ...inherent safetystable, reproducible passivating layersinfinite cyclinghigh capacitylow temperature performance
could be solved via immobile (polymer) electrolytesinherent kinetic stability
1.E-08
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
2.4 2.6 2.8 3.0 3.2 3.4
1000/T (1/K)
σ (S
/cm
)
Tm
σ = n • q • µ
Ion-conduction in polyethers
•dissolves Li salts well
•ion mobility correlated with segmental motion of the PEO chain
•crystallinity limits the conductivity below 60 °C
CH2CH2On
# of charge carriers
charge/carrier
mobility
O
OO O
O
O
OO O
O
OO
O
O
Li+
τ
O O
OO
O
O
O
O O
O
OO
O
OLi+
O
OO
O
Structures designed to limit crystallinity
•“blocky” polymers
•branched copolymers
•network polymers
Additives designed to limit crystallinity
•polymer blends
•polymer-filler composites
Limited success (10-4-10-5 S/cm @ room temperature, vs. 10-1 -10-5S/cm for liquids
Typical Approaches to Enhance Conductivity
1.E-08
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
2.4 2.6 2.8 3.0 3.2 3.4
1000/T (1/K)σ
(S/c
m)
Tm
V
s
V
s
M+
ions diffusing in a uniform potential - weak coupling limit
ion hopping: - strong coupling
highest mobility
M+chaperone approach
(a compromise)
screening layer
Idealized ion transport
"coupled" systems
σ and E derived from a single material
"de-coupled" systems
σ and E derived from separate components
composite systems -inert fillers + electrolyte
bicontinuous block copolymers
low molar mass electrolytes + inert separator
PEO/salt complexes
inorganic oxides and glasses
classifying electrolytes systems by function (mechanical, σ)
classifying electrolytes systems by function (mechanical, σ)
"coupled" systems
σ and E derived from a single material
"de-coupled" systems
σ and E derived from separate components
composite systems -inert fillers + electrolyte
bicontinuous block copolymers
low molar mass electrolytes + inert separator
PEO/salt complexes
inorganic oxides and glasses
current technology has safety issues, stuck with "canned" batteriesto be displaced by ionic liquids?
advantages for manufacture providing the morphology can be controlled. - but will the electrolyte be a liquid (high σ, but safety issues) or a polymer (low σ)
*high molecular weight and cross-linked polymers are kinetically stable - no transport to the electrode surface
classifying electrolytes systems by function (mechanical, σ
Bicontinuous phase approach to electrolytes
hydrophobic
Ion conducting matrix (hydrophilic)
• conducting phase, high σ
• network structure, mechanical stability
Si ClClCl
Cl
flame
(H2O)SiO2 n
•irregularly shaped particles
•20-100 nm in diameter
•SiOH surface groups
•aggregate in liquids and form gels
Applications:
•thickening agents for paints, coatings, cosmetics, ...
•moisture control in powders
Bicontinuous phase approach to electrolytes
hydrophobic Ion conducting matrix (hydrophilic)
• conducting phase, high σ
• network structure, mechanical stability
250 nm
V is c
o si ty
Staticperiod Shearing Static
period
Time
Driving force:
aggregates
3-D aggregates
rest
shear
primary particles
agglomerated network
phase separationH-bonding (SiOH surfaces)van der Waals (alkyl-terminated)
BASIC RESEARCH NEEDS FOR ELECTRICAL ENERGY STORAGE(DOE Workshop, 2007, http://www.sc.doe.gov/bes/reports/abstracts.html)
Cross-Cutting Science: technology challenges
Liquid electrolytes• Provide the needed high conductivity for electrochemical capacitors
but can have safety and containment issues.• Have voltage windows that limit the device performance range.• Contain electrolyte impurities that lead to degradation in performance.Electrolytes can be the weak link limiting innovations in electrode
materials, and associated power and power density.
Need new electrolytes with high ionic conductivity, low fluidity, easily purified.
Low nucleophilicity and electrophilicity - unreactive in both electron transfer and acid-base chemistry.
BASIC RESEARCH NEEDS FOR ELECTRICAL ENERGY STORAGE(DOE Workshop, 2007, http://www.sc.doe.gov/bes/reports/abstracts.html)
Cross-Cutting Science: technology challenges
"Solid" electrolytes• Difficult to combine the electrolyte and electrode separator functions in
a single material. • Modeling provides a recipe for high conductivity - polymers with low
glass transition temperatures - but low Tg polymers have poor mechanical properties.
• Two-phase materials provide a partial solution - favorable mechanical properties, but with the electrochemical characteristics and problems of low molecular weight liquid electrolytes ( electrolyte decomposition, flammability, ...).
New approaches to electrolyte design are needed that go beyond incremental improvements.
• Establish design rules that define the relationship between electrolyte structure and performance, including ion mobility, electrochemical stability new concepts for electrolytes.
• Precisely define the double layer and interaction of electrolyte and solvent at electrode surfaces. Create self healing/self regulating electrolytes for the electrode/electrolyte interface.
• Expand the range of weakly coordinating anions (BARF, carboranes, dicationic ionic liquids, ions linked by electronically conducting segments ) to broaden the spectrum of electrolytes available forbatteries and capacitors.
• Investigate electrochemical phenomena in molten salts establish electrolytes with high conductivities, stabilities, and wide potential windows.
• Establish the thermodynamic properties of electrolytes.
Cross-Cutting Science: Electrolytes for Energy Storage
Solid electrolytes• Nanoparticle composites that exploit the interstitial
space in ensembles of high surface area nanoparticles and provide conductive channels for ion transport.
• Design smart materials that respond that moderate temperature excursions within batteries, polymer layers that selectively remove lithium dendrites, or restore conductive pathways in composite electrode structures - potentially dramatic improvement in device reliability, lifetime, and safety.
Costs. Platinum (1 mg/cm²) and membrane costs. Nafion®membranes are ~$400/m²!
Water management (in PEMFCs).
too little water: dry membranes, increased resistance, failure by cracking, creating a gas "short circuit" where hydrogen and oxygen combine directly, generating heat that damages the fuel cell.
too much water: electrodes flood, preventing the reactants from reaching the catalyst.
Fuel and oxygen flow control.
Temperature management.
Limited carbon monoxide tolerance of the anode.
Advantages of high temperature operation:
• Reduce CO poisoning effect on electrode catalyst.
• Enhance reaction kinetic at higher temperature.
• Simplify water management.
Nafion, the prototype PEM
Perfluorinated polyethylene backbone affords chemical and mechanical stability; sulfonic groups attached on side chains provides mobile protons when hydrated.
Hickner, M. A.; Pivoar, B. S.; Fuel Cells, 2005, 5, 213-229Hickner, M. A.; Pivoar, B. S.; Fuel Cells 2005, 5, 213. Hsu, W. Y.; Gierke, T. D.; J. Membr. Sci. 1983, 13, 307. Mauritz, K. A.; Moore, R. B.; Chem. Rev. 2004, 104, 4535.
Limitations:
•Cost. ~$400/m2
•Poor high temperature performance (80-90 °C)
•Low conductivity at low humidity or high temperature
•CH3OH permeability
CF2 CF2 CF2CFa b
OCF2 CF
CF3
O(CF2)2 SO3H
n
Ionic clusterchannel
• Chemically stable• Mechanically stable• High conductivity
Nafion’s bicontinuous structureYang, Y. S.; Shi, Z. Q.; Holdcroft, S., Macromolecules 2004, 37, (5), 1678-1681.
Faure S, Cornet N, Gebel G, Mercier R, Pineri M, Silicon B. Proceedings of Second International Symposium on New Materials for Fuel Cell and Modern Battery Systems, Montreal, Canada, July 6-10, 1997. P. 818.
NN O
O
O O
O
NO
N O
O
OO
O
x y
SO3H
HO3S
Random incorporation of sulfonic acid groups causes uncontrolled swelling in H2O
Distribution as blocks (a la Nafion) controls swelling
Khan, A. S.; Baker, G. L.; Colson, S.; Chem. Mater, 1994, 6, 2359-2363